1. Field of the Invention
The invention relates to a process for regenerating a spent copper-based sorbent or scavenger for removing sulfur-containing compounds from hydrocarbons.
2. Description of the Art
U.S. Pat. No. 4,163,708 describes the use of composites of copper compounds and inorganic porous carriers for removing thiol impurities from hydrocarbons to prepare the hydrocarbons for catalytic reforming using platinum or platinum-containing bimetallic catalysts that are poisoned by thiol compounds. The patent teaches that spent composites may be regenerated in a three-stage regeneration process. In the first stage adhered hydrocarbons are stripped from the spent sorbent (scavenger) with a stripping gas. After the stripping, the sorbent is subjected to oxidizing conditions to oxidize residual carbon, hydrocarbon, and sulfur compounds on the sorbent. Gas containing a small volume percent of molecular oxygen at 190.degree. C. to 260.degree. C. is a suggested oxidizing medium. The third and final stage of regeneration is to subject the sorbent to a reducing atmosphere to convert copper-sulfur-oxygen moieties on the scavenger to copper oxide/copper metal and sulfur dioxide. The sulfur dioxide is carried away by the reducing gas leaving only copper oxide/copper metal on the porous carrier. Nitrogen gas containing a few volume percent hydrogen at 188.degree. C., 5.4 to 6.4 atm is suggested as a reducing medium.
Copending commonly owned U.S. application Ser. No. 367,070 describes a process for regenerating the sulfur sorbent of U.S. Pat. No. 4,163,708 in which after stripping, oxidation, and reduction, the sorbent is impregnated with a copper salt and then calcined to convert the impregnated salt to copper metal/copper oxide. This regeneration process is said to be especially useful for regenerating sorbents that do not contain an inherent catalytic oxidizing catalyst and have been used to remove primarily mercaptans from hydrocarbon feedstocks. The oxidation step in this regeneration is carried out at 400.degree. C. to 650.degree. C. The reduction step is optional and employs a reducing gas, typically nitrogen containing a few percent hydrogen at 500.degree. C. to 700.degree. C.
Yet another process for regenerating the sulfur sorbent of U.S. Pat. No. 4,163,708 is disclosed in commonly owned U.S. application Ser. No. 362,755. Its regeneration is basically a two step process in which stripped spent sorbent is oxidized to convert sulfur to a sulfate form and then purged with an inert gas at an elevated temperature which converts the sulfate to sulfur dioxide that is carried off by the inert gas. The oxidation step in this process is normally carried out at about 450.degree. C. to 650.degree. C. The inert purge step is normally carried out at 550.degree. C. to 700.degree. C.
A principal object of the present invention is to provide an alternative regeneration process to those described above.